There has been a significant increase over the last decade in the amount of renewable generation capacity connected to electrical distribution networks. In the United Kingdom, for example, many distribution networks are reaching their maximum capacity and are unable to include more renewable generation capacity without making significant investment in network reinforcement to accommodate expected generation capacity increases.
Distribution network operators often follow a ‘fit and forget’ approach to the assessment of the maximum generated power that can be received by a network from a particular network point. The ‘fit and forget’ approach amounts to identifying the worst case scenario that could take place over an extended period of time such as a year. The worst case scenario typically involves minimum demand at the same time as maximum generation. Calculation of maximum generated power according to the ‘fit and forget’ approach is illustrated with reference to FIG. 1. FIG. 1 represents a section of an electrical network 10 comprising a first bus 12 which is connected to the remaining electrical network 14 and a second bus 16 to which a generator 18 and a load 20 are connected. An electrical line 22 between the first and second buses 12, 16 has a rating of 10 MVA which is the maximum amount of apparent power that can be carried by the electrical line without causing a thermal overload. The load 20 at the second bus 16 has an annual minimum value of 2 MVA. The maximum output that can be produced by the generator 18 at the second bus 16 is therefore 12 MVA with 2 MVA of the 12 MVA being consumed locally by the load 20 and the remaining 10 MVA being conveyed over the electrical line 22. Production of more than 12 MVA by the generator 18 will breach the 10 MVA rating of the electrical line 22 and cause a thermal overload. Calculating the maximum generation capacity according to this approach will ensure that there is no violation of the thermal constraint imposed by the electrical line 22 for all different levels of consumption by the local load 20. The ‘fit and forget’ approach does, however, determine the maximum generation capacity in a conservative fashion. This is because consumption by the local load 20 will be greater than the minimum value most of the time and at such times the generator 18 is capable of producing more than 12 MVA without violating the thermal constraint imposed by the electrical line 22. It has been appreciated that the ‘fit and forget’ approach to determining maximum generated power is likely to hinder the increase in renewable generation capacity.
Active Network Management (ANM) provides for greater generation capacity to be added to an electrical network than the ‘fit and forget’ approach. According to the ANM approach the thermal load on the electrical line 22 between the first and second buses 12, 16 in FIG. 1 is monitored. When the thermal load exceeds the rating of the electrical line 22 the generator 18 output is reduced. ANM therefore involves monitoring the electrical network and controlling generation on an on-going basis. ANM offers the advantage of providing for an increase in generation capacity without violating thermal constraints and without requiring network reinforcement, such as by adding a new line of 10 MVA rating in parallel with the existing line 22.
Many approaches to ANM depend on direct measurements being made at every constraint location. Such a known approach normally requires the installation of a large number of measuring devices at a correspondingly high investment cost. A form of ANM which is operable on the basis of indirect measurement is described in WO 2011/073670. According to WO 2011/073670 a first voltage phasor measurement is made at an output from a generator and a second voltage phasor measurement is made at a location within an electrical network to which the generator provides power. A phase angle difference between the first and second voltage phasor measurements is determined. The phase angle difference reflects the impedance of the measured part of the electrical network as well as the surrounding load and generation circumstances. The determined phase angle difference is then compared with a threshold value that represents a constraint on the electrical line between the generator and the electrical network and the generator is controlled in dependence on the outcome of the comparison. The approach of WO 2011/073670 is thus operable with fewer measuring devices than other ANM approaches and thereby saves on investment cost as well as providing for a simplification of control logic required to process and act on measurements.
The present inventors have appreciated that the direct measurement approaches to ANM and the indirect measurement approach of WO 2011/073670 have shortcomings. The present invention has been devised in the light of this appreciation.
It is therefore an object for the present invention to provide a method of determining a condition of a network section comprised in an electrical power network and in particular a method of determining the condition in dependence on indirect measurement of the network section.
It is a further object for the present invention to provide apparatus for determining a condition of a network section comprised in an electrical power network and in particular apparatus for determining the condition in dependence on indirect measurement of the network section.